Our published preliminary studies indicate that pulmonary hypertension occurs in nearly one-third of adults with sickle cell disease, that it is associated with increased mortality although pulmonary artery pressures are lower than in patients with primary pulmonary hypertension, and that chronic hemolysis with nitric oxide scavenging may be a part of the pathogenesis. The present proposal is based on three postulates. First, the problem of sickle cell-associated pulmonary hypertension may begin during childhood and adolescence. Second, the pathogenesis of sickle cell-associated pulmonary hypertension may not only include the effects of chronic hemolysis, but also the consequences of chronic hypoxia related to severe anemia and repeated vaso-occlusive episodes. Pulmonary hypertension is a recognized complication of conditions marked by chronic hypoxia, and we have recently found evidence that pulmonary hypertension complicates Chuvash polycythemia, a congenital disorder of oxygen sensing in which the hypoxic response is constitutively up regulated in the absence of hypoxia and in which high hemoglobin concentrations would promote nitric oxide scavenging. Third, the pathophysiology of sickle cell-associated pulmonary hypertension may be elucidated by comparing components of the hypoxic response in patients with sickle cell disease and Chuvash polycythemia according to the presence or absence of pulmonary hypertenson. Both sickle cell disease and Chuvash polycythemia may be characterized by nitric oxide scavenging and upregulated hypoxia inducible factor, leading to stimulation of pulmonary vascular proliferative pathways that eventuate in pulmonary hypertension. Comparing specific responses in both conditions may identify shared pathways that have a central role in sickle cell-related pulmonary hypertenison. Findings to date: 1. We have evaluated 310 patients aged 320 years old with sickle cell disease under basal conditions and 54 matched controls. A hemolytic index was generated by principal component analysis of the levels of lactate dehydrogenase, aspartate aminotransferase and bilirubin and reticulocyte count. Elevated jet velocity (defined as =2.60 m/sec based on the mean2 SD in controls) occurred in 32 patients (11.0%) including one child of 3 years old. After adjustment for hemoglobin concentration, systolic blood pressure and left ventricular diastolic function, a 2 SD increase in the hemolytic index was associated with a 4.5-fold increase in the odds of elevated jet velocity (p=0.009) and oxygen saturation =98% with a 3.2-fold increase (p=0.028). Two or more episodes of acute chest syndrome had occurred in 28% of children with elevated jet velocity compared to in 13% of other children (p=0.012), more than ten units of blood had been transfused in 39% versus 18% (p=0.017) and stroke had occurred in 19% versus 11% (p=0.2). The distance walked in 6-minute walk tests did not differ significantly, but oxygen saturation declined during the tests in 68% of children with elevated jet velocity compared to in 32% of other children (p=0.0002). The study provides evidence for independent associations of elevated jet velocity with hemolysis and oxygen desaturation. Further investigations should address whether elevated jet velocity may indicate future complications and whether early intervention is beneficial. 2. Children with SCD (n = 310) and matched controls (n = 54) were prospectively enrolled under basal conditions. Participants underwent echocardiography, pulse oximetry, 6-minute walk tests, and hematologic testing. Echocardiographic measures were compared between patients with SCD and control subjects before and after adjusting for hemoglobin. Correlations of echocardiographic and clinical parameters were determined. Tricuspid regurgitation velocity (TRV) was elevated compared to controls (2.28 vs 2.10 m/s, p <0.0001). Increased TRV was associated with left ventricular diastolic diameter, hemoglobin, and estimated left atrial pressure. TRV remained elevated when controlling for left ventricular diameter and left atrial pressure. Echocardiographically derived pulmonary resistance was not significantly different between patients with SCD and controls, although it was elevated in the SCD subgroup with elevated TRV. When controlling for hemoglobin, TRV was no longer statistically different, but pulmonary insufficiency velocity, septal wall thickness, and estimated pulmonary resistance were statistically higher. TRV, pulmonary insufficiency end-diastolic velocity, and markers of increased cardiac output were correlated with indicators of adverse functional status, including history of acute chest syndrome, stroke, transfusions, and 6-minute walk distance. In conclusion, children with SCD had mildly increased TRV that was correlated with increased cardiac output and left ventricular filling pressures. Hemoglobin-adjusted analysis also suggested a contribution of primary vascular changes. 3. Low steady state haemoglobin oxygen saturation in patients with sickle cell anemia has been associated with the degree of anaemia and haemolysis. In a prospective study of children and adolescents with sickle cell disease aged 3-20 years at steady state and matched controls, 52% of 391 patients versus 24% of 63 controls had steady state oxygen saturation <99% (P <0.0001), 9% of patients versus no controls had saturation <95% (P = 0.008) and 8% of patients versus no controls had exercise-induced reduction in saturation >/=3%. Decreasing haemoglobin concentration (P </ = 0.001) and increasing haemolysis (P </ = 0.003) but not pulmonary function tests were independent predictors of both lower steady-state saturation and exercise-induced reduction in saturation. Neither history of stroke nor history of acute chest syndrome was significantly associated with lower steady-state oxygen saturation or exercise-induced reduction in saturation. Tricuspid regurgitation velocity was higher in patients with lower steady state haemoglobin oxygen saturation (P = 0.003) and with greater decline in oxygen saturation during the six-minute walk (P = 0.022). In conclusion, lower haemoglobin oxygen saturation is independently associated with increasing degrees of anaemia and haemolysis but not pulmonary function abnormalities among children and adolescents with sickle cell disease.